Terminal bushing construction



Jan. 14, 1941. A. A. SKVORTZOFF TERMINAL BUSHING CONSTRUCTION Filed Nov. 12, 1937 ilolofllfi.

WITNESSES:

INVENTOR A/exanaer ,4. Sher/1a? ATT Patented Jan. 14, 1941 UNITED STATES PATENT OFFICE TERMINAL BUSHING CONSTRUCTION Pennsylvania Application November 12, 1937, Serial No. 174,207

Claims.

The present invention relates to terminal bushings for encased high-tension electrical apparatus, such as transformers and circuit-breakers, and more particularly to an improved terminal can construction therefor.

Bushings of the type contemplated usually comprise a cylindrical shell or Weather casing of dielectric material to be mounted at one end upon the housing of the electrical apparatus and having a metallic cap closing the other end, the cap having an exposed terminal for connection to the circuit with which the apparatus is to be associated. A hollow stud extending through the shell, secured in insulated fluid-tight relation with respect to the housing end of the shell and terminating within said cap and secured thereto, encloses a terminal lead extending from such electrical apparatus for electrical connection to said cap, or the stud may be solid and used to effect the electrical connection between said apparatus and cap. The stud is usually surrounded by insulating material and the shell filled with an insulating fluid, such as oil or a flowable insulating compound; the cap being constructed to constitute an expansion chamber for the insulating fluid. With a construction of this character, variations in temperature will cause a relative movement between the metal and dielectric parts by reason of differences in the coefficients of expansion thereof. Inasmuch as this may set up destructive forces, it is usual to provide means for permitting such expansion without breaking the joints between the various parts of the bushing.

It is an object of the present invention to provide a bushing cap construction of the general character above indicated, in which the bushing stud is hollow, and in which provision is made to insure that there is no communication between the interior of the bushing and the bore of such stud in spite of relative movement between the end of the stud and the cap of the bushing.

A further object of the invention is to provide a bushing construction in which the central stud or conductor, which may be either hollow or solid, comprises two axially aligned sections having a flexible member mechanically and electrically connecting them to permit relative axial movement of one section with respect to the other.

Other objects of the invention will be apparent from the following description and from the accompanying drawing, in which:

Figure 1 is a view in elevation, partly in section, of the terminal end of a bushing embodying the 55; present invention; and,

Fig. 2 is a View similar to Fig. 1 of a modification of the construction shown in Fig. 1.

Referring to the drawing, it will be noted that only the upper end of a bushing construction embodying the invention is disclosed, but such disclosure will be sufficient, to those skilled in the art, to indicate the use for which the invention is intended and how the construction thereof may be reproduced.

The bushing construction comprises a cylinm drical shell or weather casing 2 of dielectric material, such as porcelain, which is provided with a series of circular flanges, only one of which is shown, in a usual manner, A stud 4 extends through the shell 2 and projects above the upper end thereof. This stud may be solid and constitute the conductor to be insulated or, as in the present case, it may be the hollow core of a bushing of the condenser-type which encloses a flexible conducting lead 6 from a transformer winding. 20

The shell is provided with means for mounting it on the housing of the apparatus with which it is to be used, such as a transformer or circuitbreaker, and the stud is secured in oil-tight relation with respect to the lower end of the shell. This construction is not shown, but many such constructions are quite common in the art.

The upper end of the shell is closed by a cap 8 having the lower end thereof proportioned to seat upon the end of the shell 2 with suitable gaskets I0 therebetween. The cap is maintained in position, with the gaskets I!) under compression, by means of a plurality of compression springs I2 seated upon the bottom of the cap and 35 disposed symmetrically about the stud. The springs are maintained in compression by a nut I4 threaded upon the stud to engage a plate l6 which bears upon the upper ends of the compression springs. Preferably, upstanding circular bosses 20 are formed integrally with the base of the cap 8 to center the lower convolutions of the springs l2.

Quite obviously, as the stud 4 moves with respect to the shell 2, upon change in temperature, the differential movement will be taken up in the springs l2, and a more or less constant pressure will always be exerted upon the base of the cap to maintain the gaskets I 0 under compression.

The upper end of the cap 8 is closed by a cover 2| which is suitably bolted thereto in fluid-tight relation.

With the structure described and with the shell 2 filled with insulating fiuid, as indicated, there is a possibility that upon expansion of the fluid,

some of it may leak into the bore of the stud 4, or there may be an undesirable breathing action from the stud bore into the cap 8 upon a lowering of the fluid level in the bushing. Further, since the bushing is usually filled with fluid prior to shipment and installation, a loss of fluid may result, or moisture may enter the bushing, through the stud bore during shipment or installation. This could ordinarily be cured by closing the bore, but it would be impracticable to so do under some conditions, For example, the flexible lead 6 is usually fished-through the stud when the bushing is installed which requires that the stud bore be open, and it is desirable that the lead 6 be enclosed throughout its length by the stud to its point of connection with the terminal cap 22.

To solve these problems, the cover 2| is provided with a central aperture into which is threaded a tube 24, extending on both sides of the cover. The threaded joint may be sweated or brazed to insure a fluid-tight fit. At the upper end of the tube 24, atubular plug 26 is provided, having an outstanding flange resting upon the upper edge of the device 24. A suitable fitting is secured to the end of the lead 6, having a threaded portion for receiving securing nuts 28 which bear upon the upper edge of the plug 26. The fitting and plug are so shaped that as the nuts 23 are tightened down, the fitting is drawn upwardly with a wedging action against the plug 25. The terminal cap 22 is then screwed into position with wedging surfaces 30 thereon in fluid-tight engagement.

A fitting 32 is threaded upon the upper end of the stud 4, extending toward and terminating adjacent to the lower extension of the tube 24. The bore of the fitting is provided with a tapered surface 33 which is drawn down against the edge of the stud to insure a tight fit. The adjacent edges of the fitting and tube are provided with interlocking or interfitting notches so designed that the edges may move toward and away from each other in an axial direction, but relative rotation is prevented.

In order to seal the joint between the fittings 24 and 52, a flexible diaphragm, bellows, or other flexible type of joint 34, may be provided. As a specific embodiment, the diaphragm 34 in Fig. 1 comprises upper and lower disks 36 and 38, of thin bronze sheet, having apertures therethrough adapted to receive, respectively, the adjacent ends of the tube 24 and the fitting 32. Preferably, the inner periphery of each disk is received in a notch or bears against a shoulder upon the respective fittings and is soldered or brazed thereto to make a fluid-tight joint. The outer peripheries of the disk are in engagement and are suitably brazed, soldered, or otherwise secured to make a fluid-tight joint.

In the event of relative movement between the stud 4 and the other parts of the bushing, the stud is free to move axially thereof but not laterally or radially and at all times communication between the bore of the stud and the cap 8 is prevented because the diaphragm or bellows 34 maintains a fluid-tight joint between the ends of the tube 24 and the fitting.

The diaphragm discs 35 and 38 may be formed of copper, brass, bronze, or other suitable material and may, in fact, be a non-metallic material which is impervious to the insulating medium within the bushing. In the event that metal is used, the disks may be formed separately and se cured together as shown, or the structure may be formed of a continuous seamless tube spun to the desired shape.

In the event that it is desired to inspect the interior of the cap, the terminal 22 may be unscrewed, and the conductor 6 lowered by removing the nuts 28. The bolts which clamp the cover 2! to the body of the cap may then be removed, and the cover, tube 24, diaphragm and fitting 32 may be removed as a unit by unscrewing the assembly from the top of stud 4. By this means the joint between the cover and tube 24 is not disturbed, and by reason of the sliding joint between the end of the tube and fitting 32, relative rotation between these members is prevented so that distortion of the diaphragm 34 with resultant injury to it is avoided. Obviously, this feature is important in connection with both the assembly and disassembly of the bushing.

Further, the diaphragm mounting has the advantage that it facilitates inspection of the cap interior in that no part of it is secured to the body of cap 8, and it is removable with the cover 21'. The present construction results, in effect, in a two piece bushing stud having the remote ends thereof in fluid-tight relation with respect to the interior of the bushing, and a flexible fluid-tight joint between the adjacent ends having no connection with the walls of the cap.

The construction shown in Fig. 2 illustrates the invention applied to a bushing having a solid stud 4%) the upper end of which cooperates with a tube 42, suitably brazed (as indicated) or sweated to the cover 44, in a manner similar to the hollow stud 4 and tube 24 of Fig. 1. The lower end of tube 42 and the upper edge of a fitting 43 on the end of the stud 40 are provided with interlocking notches similar to those previously described. A diaphragm or bellows 46 of modified form constitutes a flexible connection between the fitting 43 and tube 42 to permit relative axial movement of the parts and constitute the electrical connection between the stud 40 and the terminal 48, as well as to prevent the loss of fluid up through the tube 42 and past the joint with the terminal 48. Here again the cap 44, tube 42, diaphragm 46 and fitting 43 are assembled as a unit and may be removed as a unit to afford free access to the interior of the cap. Of course if the tube 42 is also solid and in good oil-tight relation with the cover 44, the diaphragm may be omitted and a flexible jumper used to make the electrical connection, the jumper being of such length that it may be connected to the stud and solid tube 42 before the cover is secured in place.

In view of the many modifications that may be made in the invention without departing from the spirit thereof, it is intended that the scope of the invention be limited only by the scope of the appended claims.

I claim as my invention:

1. In a bushing for high-tension electrical apparatus including a shell of dielectric material having a hollow stud extending therethrough, a. cap for closing the end of said shell and enclosing the end of said stud, and means for so mounting said stud with respect to said shell that said end of said stud is free to move axially thereof with respect to said end of said shell; a connector between the upper end of said stud and the top of said cap comprising two tubular members in substantial alignment with each other and with said stud, means for securing the remote end of one of said members to said cap, means for securing the remote end of the other of said members to the end of said stud by a rotary movement, and a fluid-tight flexible member connecting the adjacent ends of said members, the securing means between said remote ends and the cap and stud as well as the connection between said adjacent ends being fluid-tight to prevent communication between the interior of the cap and the bore of the stud, and means for preventing one of said adjacent ends from rotating with respect to the other comprising interengaging means on said ends slidable with respect to each other axially of the tubular members and interlocked against relative rotation.

2. In a bushing for high-tension electrical apparatus including a shell of dielectric material having a hollow stud extending therethrough, a cap having a removable cover for closing the end of said shell and enclosing the end of said stud, and means for so mounting said stud with respect to said shell that said end of said stud is free to move axially thereof with respect to said end of said shell; a connector between the upper end of said stud and the top of said cap comprising two tubular members in substantial alignment having the remote end of one secured to the cap and the remote end of the other removably secured to the stud in fluid-tight relation, a fluid-tight flexible member connecting the adjacent ends of said members so that communication between the interior of the cap and the bore of the stud is prevented, and means connecting the adjacent ends of said members whereby the connector may be detached from said stud by manipulation of said cover.

3. In a bushing for high-tension electrical apparatus including a shell of dielectric material having a stud extending therethrough, a cap having a removable cover for closing the end of said shell and enclosing the end of said stud, and means for so mounting said stud with respect to said shell that said end of said stud is free to move axially thereof with respect to said end of said shell; means depending from said cover for connection with said stud comprising a tubular member and means for removably securing one end thereof to said stud by a rotary movement, a second tubular member and means for securing one end thereof to said cover, said tubular members being disposed in alignment, means for conmeeting the free ends of said tubular members comprising an interfitted joint so formed that the members are interlocked against relative rotation and may move relative to each other axially of said' stud, and flexible means surrounding said joint and hermetically sealed to said tubular members.

4. In a bushing for high-tension electrical apparatus including a shell of dielectric material having a hollow stud extending therethrough, a

cap having a removable top for closing the end of said shell and enclosing the end of said stud, and means for s0 mounting said stud with respect to said shell that said end of said stud is free to move axially thereof with respect to said end of said shell; a connector between the upper end of said stud and the top of said cap comprising a. cylindrical fitting within said cap depending from the top thereof in substantial alignment with said stud, a tubular member and means for removably securing one end thereof by a rotary movement to the free end of said stud in fluid-tight relation with the other end of the member extending adjacent tothe free end of said fitting, means including a fluid-tight flexible member defining a chamber enclosing the free ends of said fitting and tubular member to prevent communication between the interior of the cap and the bore of 1 said stud and means on the adjacent ends of said tubular member and cylndrical fitting interlockin said member and fitting against relative rotation and permitting relative movement therebetween in a direction axially of said stud.

5. In a bushing for high-tension electrical apparatus including a shell of dielectric material having a hollow stud extending therethrough, a cap having a removable top for closing the end of said shell and enclosing the end of said stud, and means for so mounting said stud with respect to said shell that said end of said stud is free .to move axially thereof with respect to said end of said shell; a connector between the upper end of said stud and the top of said cap comprising a tubular member removably threaded at one end to the end of said stud to constitute'an extension thereof, a fitting secured to said removable top of the cap and extending adjacent to the free end of said member, fluid impervious means enclosing said free end of said member of a portion of said fitting in fluid-tight relation, and a joint between said free end and portion interposing a sliding resistance to relative movement between the tubular member and fitting longitudinally of the axis of the stud and a positive resistance against relative rotation therebetween.

ALEXANDER A. SKVORTZOFF. 

